The invention relates to an internal gear pump for pumping fuel from a suction conduit into a pressure conduit, having a pump housing in which an internal ring gear and an externally toothed pinion, the latter driven by a drive shaft, are supported, the pinion being disposed eccentrically to the ring gear and cooperating with the ring gear to generate a pumping action, and the pinion and the ring gear rest with their one face end on the pump housing and with their other face end on a sealing plate.
An internal gear pump of this kind is also called a ring gear pump or gear-rotor pump. The ring gear and the pinion represent the pump elements and are also called the outer rotor and the inner rotor, respectively. In German Patent Disclosure DE 38 27 573 A1, an internal gear pump is described whose ring gear is driven via an electric motor. The pumping chambers of the internal gear pump that are located between the sets of teeth of the two pump elements are covered in the axial direction by a pressure plate. A helical spring, embodied as a compression spring, which is prestressed against the pressure plate assures that the axial play equals zero when the internal combustion engine is started.
When an internal combustion engine is operated with an internal gear pump of this kind, it has been found that upon engine starting, the maximum pumping capacity of the internal gear pump is required. Once the engine has reached its full rpm, a lesser pumping capacity suffices to assure an adequate fuel supply to the engine.
The object of the invention is to furnish an internal gear pump of the type defined at the outset, which has zero axial play at starting rpm and whose pumping capacity decreases once the starting rpm has been exceeded. It should be possible to produce the internal gear pump of the invention economically, and the pump should have a long service life.
In an internal gear pump for pumping fuel from a suction conduit into a pressure conduit, having a pump housing in which an internal ring gear and an externally toothed pinion, the latter driven by a drive shaft, are supported, the pinion being disposed eccentrically to the ring gear and cooperating with the ring gear to generate a pumping action, and the pinion and the ring gear rest with their one face end on the pump housing and with their other face end on a sealing plate, this object is attained in that the suction conduit is disposed in the sealing plate, and that the sealing plate is movable relative to the pump housing in such a way that the spacing between the suction conduit and the pressure conduit can be varied.
If the spacing between the suction conduit and the pressure conduit is decreased, the consequence is that the pumping capacity of the internal gear pump decreases. This offers the advantage that an intake throttle, required in conventional internal gear pumps, can be dispensed with.
A particular feature of the invention is characterized in that the suction conduit is formed by an elongated recess in the circumferential direction of the sealing plate, and that the sealing plate is rotatable relative to the pump housing between two points.
A further particular feature of the invention is characterized in that the sealing plate is prestressed in the axial direction with the aid of a spring, which is coupled to the pump housing and to the sealing plate. By the spring prestressing in the axial direction, it is attained that a motion of the sealing plate in the axial direction does not occur until a certain pressure in the pump chamber has been exceeded.
A further particular feature of the invention is characterized in that the spring is prestressed in the circumferential direction counter to the driving direction of the internal gear pump. Because of the spring prestressing in the circumferential direction, it is attained that the sealing plate does not rotate until a certain rpm of the pinion has been exceeded.
A further particular feature of the invention is characterized in that the spring includes two curved legs, which on one end are joined together and coupled to the sealing plate, and on the other end are coupled to the pump housing. By the design according to the invention of the spring, a prestressing of the spring both in the axial direction and in the circumferential direction is made possible by simple means.
A further particular feature of the invention is characterized in that on the side of the sealing plate remote from the ring gear and the pinion, a pin is guided axially displaceably at a certain spacing, which pin cooperates with a further spring in order to counteract a motion of the sealing plate in the axial direction. The spacing between the sealing plate and the pin is selected such that the sealing plate comes to rest on one face end of the pin in full-load operation. If the pressure in the pump chamber rises further, the sealing plate moves farther counter to the prestressing force of the further spring. The prestressing force of the further spring, its spring rate, and the displacement of the sealing plate in the axial direction up to a stop define the maximum operating pressure of the internal gear pump.
A further particular version of the invention is characterized in that the suction conduit communicates with a fuel inlet, whose longitudinal axis coincides with the longitudinal axis of the drive shaft. This design has proved to be especially advantageous in practice.
A further particular feature of the invention is characterized in that the fuel inlet discharges into a sleeve, in which the further spring is received, and in which radial bores are mounted for the passage therethrough of fuel. The sleeve forms a stop that defines the axial motion of the sealing plate.
A further particular feature of the invention is characterized in that a bypass valve is accommodated in the pump housing and communicates with the suction conduit via a first axial bore and with the pressure conduit via a second axial bore. Within the context of the present invention, xe2x80x9caxialxe2x80x9d means in the direction of the longitudinal axis of the drive shaft of the internal gear pump. The bypass valve makes it possible, for instance with the aid of an additional hand-actuated pump, to pump the fuel in a way that bypasses the internal gear pump when the internal gear pump is not being driven.
Further advantages, characteristics and details of the invention will become apparent from the ensuing description, in which one exemplary embodiment of the invention is described in detail in conjunction with the drawing. The characteristics recited in the claims and mentioned in the description can each be essential to the invention individually or in arbitrary combination.